Quantum computing and the entanglement frontier
John Preskill Caltech Board of Trustees 31 October 2015
Quantum Information Science
quantum theory Planck + computer science + information theory
Turing quantum information science
Shannon Caltech and Information Science
Nanotechnology: “There’s plenty of room at the bottom.” Feynman
Very-Large-Scale Integration (VLSI): Paradigms for the semiconductor industry.
Mead
Computation & Neural Systems (CNS): How does the brain compute?
Hopfield Frontiers of Physics short distance long distance complexity
Higgs boson Large scale structure “More is different”
Neutrino masses Cosmic microwave Many-body entanglement background Supersymmetry Phases of quantum Dark matter matter Quantum gravity Dark energy Quantum computing String theory Gravitational waves Quantum spacetime ???
Quantum Supremacy! Shell Game Shell Game Shell Game Shell Game Shell Game Shell Game
1 2 3
When the Gorilla give thumbs up, and you look under Cup Number 1, you always find the ball. Shell Game
?
1 2 3
What if the Gorilla gives thumbs up, and you look under Cup Number 2? (Classical) Shell Game
When the Gorilla gives thumbs up & you look under Cup Number 1, you always find ball.
?
When the Gorilla gives thumbs up & you look under Cup Number 2, you find the ball ... A. Always B. Never C. Sometimes (Classical) Shell Game
When the Gorilla gives thumbs up & you look under Cup Number 1, you always find ball.
When the Gorilla gives thumbs up & you look under Cup Number 2, you find the ball ... A. Always B. Never C. Sometimes (Quantum) Shell Game
When the Gorilla gives thumbs up & you look under Cup Number 1, you always find ball.
?
When the Gorilla gives thumbs up & you look under Cup Number 2, you find the ball ... A. Always B. Never C. Sometimes (Quantum) Shell Game
When the Gorilla gives thumbs up & you look under Cup Number 1, you always find ball.
When the Gorilla gives thumbs up & you look under Cup Number 2, you find the ball ... A. Always B. Never C. Sometimes (Quantum) Shell Game
Secret of the Quantum Gorilla: Before deciding whether to give thumbs up, he checks the cups collectively , rather than one at a time. Quantum entanglement
…. This This This This This …. Page Page Page Page Page Blank Blank Blank Blank Blank
Nearly all the information in a typical entangled “quantum book” is encoded in the correlations among the “pages”.
You can't access the information if you read the book one page at a time. To describe 300 quantum bits (e.g., atoms), we would need more numbers than the number of atoms in the visible universe! Caltech Course 1983-84:
Potentialities and Limitations of Computing Machines
“Nature isn't classical, dammit, and if you want to make a simulation of nature, you'd better make it quantum mechanical.” Problems
Quantumly Hard
Quantumly Easy
Classically Easy
What’s in here? particle collision molecular chemistry entangled electrons
A quantum computer can simulate efficiently any physical process that occurs in Nature. (Maybe. We don’t actually know for sure.)
superconductor black hole early universe Decoherence
1 2 ( + ) Environment Quantum Computer Decoherence Environment
To avoid errors, we must prevent the environment from “learning” about the state of ERROR! the quantum computer during the computation. Quantum error correction
…. This This This This This …. Page Page Page Page Page Blank Blank Blank Blank Blank
Environment
The protected “logical” quantum information is encoded in a highly entangled state of many physical qubits.
The environment can't access this information if it interacts locally with the protected system. Kitaev’s magic trick: sawing an electron in half! Alexei Kitaev
Jason Alicea
Gil Refael Institute for Quantum Information (IQI): Postdoc Alumni
Eddy Ardonne Nordita Robert Koenig Munich Salman Beigi IPM Debbie Leung Waterloo Robin Blume-Kohout Sandia NetanelLindner Technion SougatoBose UC London Yi-Kai Liu NIST Sergio Boixo Google Ashwin Nayak Waterloo Sergey Bravyi IBM Stefano Pironio Brussels Darrick Chang ICFO David Poulin Sherbrooke Andrew Childs Maryland Robert Raussendorf UBC Andrew Doherty Sydney Ben Reichardt USC LumingDuan Michigan Norbert Schuch Aachen Omar Fawzi ENS Lyon YaoyunShi Michigan Lukasz Fidkowski Stony Brook Kirill Shtengel UC Riverside Steve Flammia Sydney KristanTemme IBM Alexei Gorshkov NIST Barbara Terhal Aachen David Gossett IBM Frank Verstraete Vienna Sean Hallgren Penn State GuifreVidal Perimeter Patrick Hayden Stanford Ling Wang Beijing Liang Jiang Yale Stephanie Wehner Delft Stephen Jordan NIST Pawel Wocjan UCF Liang Kong Tsinghua ShengyuZhang Hong Kong 40 former IQI postdocs hold faculty positions (or the equivalent). 18 US, 5 Canada, 10 Europe, 3 Asia, 2 Australia, 2 Middle East.
Challenging the entanglement frontier!
Quantum Information Quantum Matter
Surface -spin Quantum Optics Mechanical Quantum Systems
γ γ
1 atom Jason Alicea, 2012 David Hsieh, 2012 Andre Faraon, 2012 Xie Chen, 2014 Quantum Matter Quantum Matter Quantum Optics Quantum Matter Theory Experiment Experiment Theory (Physics) (Physics) (Applied Physics) (Physics)
Thomas Vidick, 2014 Manuel Endres, 2016 Fernando Brandão, 2016 Stevan Nadj-Perge, 2016 Quantum Information Quantum Optics Quantum Information Quantum Matter Theory Experiment Theory Experiment (Computer Science) (Physics) (Physics) (Applied Physics) IQIM Annual Retreat iqim.caltech.edu/outreach
IQIM quantum animations in collaboration with Jorge Cham of PHD Comics. Over 1 million views so far! Unveiling the qCraft mod to MineCraft at MineCon 2013. qCraft has been downloaded over 3 million times from qcraft.org
WHAT’S INSIDE A BLACK HOLE? Holographic Principle
All information inside the room is encoded, in a scrambled form, on the boundary of the room. Holographic Principle
This scrambled encoding may be a quantum error- correcting code. The emergent space inside the room is robust against errors on the walls of the room. Holographic Principle
Quantum entanglement holds space together. Richard Feynman
(Quantum) Shell Game
When the Gorilla gives thumbs up & you look under Cup Number 1, you always find ball.
When the Gorilla gives thumbs up & you look under Cup Number 2, you find the ball ... A. Always B. Never C. Sometimes From: Robert Dijkgraaf at the inauguration of Caltech’s Burke Institute. From: Robert Dijkgraaf at the inauguration of Caltech’s Burke Institute.
Additional Slides Frontiers of Physics short distance long distance complexity
Higgs boson Large scale structure “More is different”
Neutrino masses Cosmic microwave Many-body entanglement background Supersymmetry Phases of quantum Dark matter matter Quantum gravity Dark energy Quantum computing String theory Gravitational waves Quantum spacetime Peter Shor Finding Prime Factors
1807082088687 4048059516561 6440590556627 8102516769401 3491701270214 5005666254024 = ? × ? 4048387341127 5908123033717 8188796656318 2013214880557 Finding Prime Factors
1807082088687 4048059516561 6440590556627 3968599945959 4553449864673 8102516769401 7454290161126 5972188403686 3491701270214 = 1628837860675 8972744088643 5005666254024 7644911281006 × 5630126320506 4048387341127 4832555157243 9600999044599 5908123033717 8188796656318 The boundary between 2013214880557 “hard” and “easy” seems to be different in a quantum world than in a classical world. Shor Majorana topological Majorana fermion superconductor fermion
conventional conventional superconductor superconductor Majorana topological Majorana fermion superconductor fermion
conventional conventional superconductor superconductor
add an electron Majorana topological Majorana fermion superconductor fermion
conventional conventional superconductor superconductor Majorana topological Majorana fermion superconductor fermion
conventional conventional superconductor superconductor
conventional superconductor topological Majorana superconductor fermion
conventional conventional superconductor superconductor
Majorana fermion conventional superconductor Majorana topological fermion superconductor
conventional conventional superconductor superconductor
Majorana fermion conventional superconductor Majorana topological Majorana fermion superconductor fermion
conventional conventional superconductor superconductor
conventional superconductor Alexei Kitaev Topology
Quantum Quantum Computer Computer
Noise! Φ Φ Φ
Aharonov-Bohm exp(ie Φ) Phase Φ
Aharonov-Bohm exp(ie Φ) Phase Anyons
Quantum information can be stored in the collective state of exotic particles in two spatial dimensions (“anyons”).
The information can be processed by exchanging the positions of the anyons (even though the anyons never come close to one another). Anyons
Quantum information can be stored in the collective state of exotic particles in two spatial dimensions (“anyons”).
The information can be processed by exchanging the positions of the anyons (even though the anyons never come close to one another). Topological quantum computation
annihilate pairs?
braid Kitaev braid
braid time create pairs Topological quantum computation
annihilate pairs?
braid Kitaev braid
braid time create pairs Topological quantum computation
The computation is intrinsically resistant to decoherence. If the paths followed by the particles in spacetime execute the right braid, then the quantum computation is guaranteed to give the right answer! time Alexei exhibits a knack for persuading That someday we’ll crunch quantum data by braiding, With quantum states hidden where no one can see, Protected from damage through topology.
Anyon, anyon, where do you roam? Braid for a while … before you go home.
Etc. Quantum Computer Decoherence Environment
If a quantum computation works, and you ask the quantum computer later what it ERROR! just did, it should answer: “I forget...” Decoherence
1 2 ( + ) Environment
Decoherence explains why quantum phenomena, though observable in the microscopic systems studied in the physics lab, are not manifest in the macroscopic physical systems that we encounter in our ordinary experience. Weekly seminar and reception organized by IQIM students and postdocs Jeff Kimble Professor H. J. Kimble Is much larger than a thimble And a veritable symbol Of the physicist today.
Could it be prodigious height Explains his knack for squeezing light Or is Jeff’s mind extremely bright? I guess that’s hard to say…
Etc. Caltech quantum information
Jeff Kimble John Preskill Physics Physics
Alexei Kitaev Leonard Schulman Physics, Math, and Computer Science Computer Science
Gil Refael Physics Quantum Information Challenges
Cryptography Algorithms ∑|x〉⊗ |() f x 〉 x∈ G
Privacy from physical principles What can quantum computers do? Error correction Hardware
Quantum Computer Noise
Reliable quantum computers Toward scalable devices And …what are the implications of these ideas for basic physics? iqim.caltech.edu Talk is supposed to be 25 minutes. Halloween gag. Feynman Nobel. Jubilee year for Bell. The Delft experiment in NYT. Exp highlights from IQIM. Making quantum weirdness macroscopic. One Entangled Evening. Hawking was at Caltech when he formulated information paradox. Spacetime is made from entanglement … so we can take a bite out of the boundary Students and postdocs are crucial. Something about Outreach? Qcraft. Studying quantum gravity with quantum computers. Caltech investment in young faculty: Brandao, Endres, Nadj-perge, Chen, Alicea, Hsieh, Faraon, Vidick
Theme: the unity of physics.
Dijkgraaf slide on quantum information. Gorilla. Evolution of physics.
Use Eric Mazur’s method. A quantum question. Quantum shell game. Even quantum biology. PARADOX! When the theories we use to describe Nature lead to unacceptable or self-contradictory conclusions, we are faced with a great challenges and great opportunities…. Planck Hawking 1900 1975 “The ultraviolet catastrophe ” “The information loss puzzle ” In thermal equilibrium at nonzero The radiation emitted by an temperature, the elelctromagnetic evaporating black hole is featureless, field carries an infinite energy per revealing nothing about how the unit volume … black hole formed …
The end of The end of quantum physics? classical physics! (Or of relativistic causality?) Building spacetime from quantum entanglement
AB A B = Wormhole Entanglement
AB A B = No Wormhole No Entanglement Love in a wormhole throat singularity
Alice Bob
time
Alice and Bob are in different galaxies, but each lives near a black hole, and their black holes are connected by a wormhole. If both jump into their black holes, they can enjoy each other’s company for a while before meeting a tragic end. Is spacetime a quantum error- correcting code? Pastawski, Yoshida, Harlow, Preskill = HaPPY arXiv:1503.06237
John Preskill, Caltech RQI-N-2015, Dartmouth 5 July 2015 Is spacetime a quantum error-correcting code?
Local “logical” operators in the bulk mapped to nonlocal “physical” operators on the boundary which are well protected against erasure of boundary degrees of freedom. [Pastawski-Yoshida - Harlow-Preskill 2015]
Bulk operators in the “entanglement wedge” of (disconnected) boundary region A can be reconstructed on A. [Headrick et al. 2014]
erased regions “Now is the time for quantum information scientists to jump into .. black holes” Beni Yoshida QuantumFrontiers.com March 2015 Quantumists ≈ Biologists quantum gravity = life boundary theory = chemistry quantum information theorists = chemists quantum gravity theorists = biologists what we want = molecular biology black hole information problem = fruit fly understanding the big bang = curing cancer
Slide concept stolen from Juan Maldacena Ooguri : I see that this new joint activity between quantum gravity and quantum information theory has become very exciting. Clearly entanglement must have something to say about the emergence of spacetime in this context.
Witten : I hope so. I’m afraid it’s hard to work on , so in fact I’ve worked with more familiar kinds of questions.
Kavli IPMU News December 2014
Notices of AMS May 2015 Caltech and Information Science
Feynman As we run out of “room at the bottom,” the world needs visionary ideas about how physical systems can store and process information. Providing those ideas, and training Mead the people who will put them into practice, is part of the mission of IST.
Hopfield Quantum Information Science
Quantum physics, information theory, and computer science Planck are among the crowning intellectual achievements of the 20th century.
Quantum information science is an emerging synthesis of these themes, which is Turing providing important insights into fundamental issues at the interface of computation and physical science, and may guide the way to revolutionary technological advances. Shannon Big Questions HEP: What underlying theory explains the observed elementary particles and their interactions, including gravity?
QIS: Can we control complex quantum systems and if so what are the scientific and technological implications? Not the frontier of short (subnuclear) distances or long (cosmological) distances, but rather the frontier of highly complex quantum states: The entanglement frontier Also: emergence of classicality, security of quantum cryptographic protocols, foundations of statistical mechanics and thermalization, information theoretic principles illuminating the foundations of quantum physics, information processing by e.g. black holes, etc. Truism: the macroscopic world is classical. the microscopic world is quantum. Goal of QIS: controllable quantum behavior in scalable systems Why? Classical systems cannot simulate quantum systems efficiently (a widely believed but unproven conjecture). But to control quantum systems we must slay the dragon of decoherence … Is this merely really, really hard ? Or is it ridiculously hard? 9 April 1997 … An exciting day! You and your buddy were made in a pair, Then wandered around, braiding here, braiding there. You’ll fuse back together when braiding is through Well bid you adieu as you vanish from view.
Alexei exhibits a knack for persuading That someday we’ll crunch quantum data by braiding, With quantum states hidden where no one can see, Protected from damage through topology.
Anyon, anyon, where do you roam? Braid for a while … before you go home.
Etc. Alexei exhibits a knack for persuading That someday we’ll crunch quantum data by braiding, With quantum states hidden where no one can see, Protected from damage through topology.
Anyon, anyon, where do you roam? Braid for a while … before you go home.
Etc.